Discharge lamp circuit



May 18, 1948. J. H. CAMPBELL 2,441,796

DISCHARGE LAMP CIRCUIT Filed Oct. 23, 1945 INVENTOR 1 JOHN H. CAMPBELL,

BY MM'AJE m M.

HIS ATTORNEY.

atenteri May 18, 194 8 UNI John H. Gampbell; Altamont; N; Y., assign'or to General Electric, Company; a corporaltiox't' or New York.

1V invention relates to electric discharge devices and their circuits, and especially tg't'h'e leading power-factor units of two-lamp lead and lag. circuits. An important aimof the invention is to assure adequate current for preheating the cathodes of lamps in leading circuits be-- This fore the arc discharge is initiatedbet-ween the cathodes, and particularly cathodes embodying heating means through which the preheat cur rent passes. The invention is hereinafter ex:- plained. with particular reference to fluorescent lamps of the ordinary low" pressure positive column electricv discharge type;

In usual. practice, a fluorescent lamp] such as here referred to is connected across an; A.- C; operating or discharge circuit. that includes;

inductive ballast. for controlling and regulating the discharge current during: operation; A starting. circuit is connected: across the" operating:

circuit in parallel with" the: discharge gap? be;-

tween the electrodes, through: their' heating means aforementioned; and includes a starting switch (manual or automatic) by which, the;

starting circuit, is suddenly interrupted; aftericurrent flow therein has brought. the electrodes to;

a temperature of adequatev thermionic-emission;

Owing to the inductive ballast in the. operating: circuit, this sudden opening of the startingv cir.- cuit results in a high voltage kick between, the electrodes, which usually suffices. to initiate; the:

discharge.

During the cathode-preheating period; beforev initiation of the discharge, the; inductive ballast in the operating circuit naturally tends to -keep down the preheating current in the starting cir-- cuit. In the case of a leading power factorcircuitwhichincludes a capacitor or condenser/in series with the inductiveiballastaforementioned, the. pre-heating current; under these conditions; is little if any greater than the discharge cure;

rent after starting, and does not suffice to? preheat the cathodes quickly. and adequately. Itis therefore usual in such cases to include an; in-

ductive choke coil or" compensator 'in-thestarting circuit in series with itsswitch, to 'cqact with; the inductive ballast and: the capacitor. of; the; operating circuit in bringing the combined cir-- cuit intorat least partial resonance, 1 and thus'give:

a greater preheatingcurrent.

My; invention; allows.- of dispensing with: such 2- a .Qmpe,n'satorv in the starting circuit without an ommenta'd" i eni' 9i he y t m; nu simplifying it a'ndfreducing its cost". "The s'ingllcfigure' of the drawing is a; diagrarn of} lamp; circuit arrangements embodying" the nl'eniim T e rew n I Q w; r s ur posit v 9 urnn'fdl' harge la 'np':- l consisting of an: envelope we t ide ed" q r'e t iifis eiectro'd 2f; 2 infits cpposite ends, Either or secr tes 1'': a be h i i lb activated cathode:

a suppl f mean-t is indicated by a ilet" 3i Also, an internalcoating fjifu'm negcent material or phosphor '4' excitableb the radiationfrom th;

e is m cca i h nie ei w'a'hi.

As shown; the v electrodes "1', 2" areconnected to; oprm t de iof re a" r" e i igrireui Sfvjvhich may be th leading branch of 'atw;on p; lead" and lagcircuit "(the otherbranch of which is not shown a includes the inductive" balla or reactor cangi the cap citorl series wit another and with the discharge, device v f I', as. usual in. such lead circuits. The: dis:

H H a w t i; a be: 0i m su l; P 5

circuit 5; maybe energized from, suitahle source; such as a' lli0i fio volt 6 0 cycle A circuit; notQshow-n, v A man? control s'w itch 8' is also shown, for, control]; energization of the circuit, 5I" starting, circuit 9 is shown connected across the T discharge circu t 5c in parallel with the; lamp. l between and through the @cathode eoils or resistance heaters aiafwiui startinglsiwitchr l l ljtherein T is? charge s ur t enfb i i 9 u enl i t n tzflueq quit efiien the rs nt through he qi at;:hhaaheat dfinih :qeihcsics to: azjtempe atme Qfi'asieq aiez leqhqn"emi si, a

anua reutqma xm thus producing a voltage kick across the lamp I which starts the discharge.

In accordance with my invention, a capacitor II is connected into one side of the discharge circuit 5 in shunt with reactive ballast represented by the choke 6, but in series with the lamp I and capacitor 7. The inductance 6 and capacitor H form a loop circuit whose resonance frequency depends (other things being equal) on the value of the current in the discharge circuit 5. The reactor or inductance 6 and the series capacitor I are chosen on the basis of giving a suitable or optimum current through the cathode coils 2, 2 for preheating the cathodes quickly and adequately before the arc discharge between these electrodes is initiated, but without regard to the wattage that they would by themselves give in actorB is so chosen or designed that its reactive characteristic with varying current is non-linear;

The capacitor I I is so chosen that it does not materially affect the preheating current that flows while the starting switch I is closed, so that the cathodes 2, 2 heat rapidly, permitting a relatively prompt, quick start of the lamp I after the discharge circuit 5 is energized. During lamp operation, on the other hand, When the much greater resistance or impedance of the discharge path in the device I is substituted across the dis,

charge circuit 5, the current in the circuit is lower than during starting. This is brought about by a decrease in saturation of the choke 6,'which in combination with the capacitor II presents a higher effective'impedance than during starting. The loop circuit including them is then closer to resonance. Hence the discharge current and the lamp wattage are kept down to the desired normal operating values atthe line voltage center.

For the convenience of those wishing to use my invention, I give illustrative values of circuit constants suitable for an ordinary commercial 30 watt positive column fluorescent lamp of usual 36 inch tube length and 1 inch diameter; but these are not to be understood as defining or limiting the invention in its broader aspects. For example, the inductance 6 may be wound to give a 118 volt drop on a GO-cycle A. C. current of .34 ampR. M. S., with a D. C, resistance of 7 ohms; and the capacitors I and II may have capacities of 4 mid. and mfd. respectively. The cathode coils 2, 2 of the lamp I are assumed to be of the usual coiled coils of the 30 watt lamp above mentioned, each comprising an active length of252 mm. of 2.85 mil diameter tungsten wire. For a supply voltage of 118 across the line or operating circuit 5, the cathode preheating current before starting will be 0.48 amp., against an operating voltage of 0.34 amp. after starting.

It will be understood that the values of circuit constants given are illustrative, and that even the circuits shown can be varied in some particulars, such as the portion of the operating circuit 5 shunted by the capacitor II E, g., this capacitor II might shunt only part of the inductance or reactive ballast 6. V

, WhatI claim as new and desire to secure by LettersPatent of the United Statesis:

1. For an electric discharge device having thermionic electrode means including electric heating means and a starting circuit connected to said heating means and across the gap be tween said electrode means, a leading powerfactor operating circuit connected to said elec trode and heating means including capacitance and reactive ballast of non-linear reactive char- 4 acteristic with current in series with one another, a starting switch connected across said discharge device and means for reducing the current transmitted to said discharge device after opening said 5 switch upon initiation of a discharge within said device including capacitance in parallel with re active ballast aforesaid to constitute therewith a parallel circuit approaching resonance.

2. In combination, an electric discharge device 10 having thermionic electrode means including electric heating means, a leading power factor operating circuit connected to said electrode and heating means and including capacitance and reactive ballast of non-linear reactive characteristic with current in series with one another, a

starting circuit including an interrupting switch connected to said heating means and across the the lamp I during ordinary operation. The reelectrode means, the impedance of said ballast being substantially smaller when said switch is closed than when open, and means for limiting the current transmitted to said discharge device -to a value less than that which would be established by the increased impedance of said ballast incident to reduced current flow occasioned by opening said switch comprising a capacitor connected across said ballast and constituting therewith a parallel circuit approaching resonance.

3. In combination, an alternating current circuit, an electric discharge device comprising a pair of electrodes at least one of which is of the thermionic type, a starting switch connected across said electrodes, a serially connected capacitor and a non-linear inductive ballast connected between one terminal of said circuit and one of said electrodes, said ballast having a relatively small impedance during a starting operation wherein substantial starting current is trans-' mitted through the thermionic electrode upon closure of said switch, the other electrode being 40 connected tothe other terminal of said circuit,

and after opening said switch, constitutes a circuit tuned to approach the frequency of said circuit in order to limit the current supplied to the discharge device during operating conditions.

4. In combination, an alternating current sup- 5 ply circuit, an electric discharge device having a pair of thermionic electrodes each provided with heating means, a leading power-factor circuit connected between one terminal of said supply circuit and one of said heating means and com- 65 prising a serially connected capacitor and a nonlinearinductive ballast, a starting switch connected directly across said electrodes and which upon closure effects the transmission of heating current in series relation through the heating means for said pair of electrodes, and means for controlling the current transmitted to said discharge device after initiation of a discharge between said electrodes and after opening said switch and comprising a capacitance connected across said ballast. to constitute therewith a parallel circuit approaching resonance to limit the current transmitted during normal operating conditions.

5. In combination, an alternating current supply circuit, an electric discharge device having a pair of thermionic electrodes of the filamentary V type, a leading power-factor circuit including a serially connected inductive ballast and a capacitor connected between one terminal of said supply circuit and one of said electrodes, means comprising a starting switch connected across said electrodes for effecting transmission of starting current from said supply circuit through said electrodes and said ballast and capacitor, and means for reducing the current transmitted to said discharge device upon initiation of a dis charge between said electrodes and after opening said switch comprising a capacitor connected across said ballast to constitute therewith a parallel circuit approaching resonance.

JOHN H. CAMPBELL.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number 6 UNITED STATES PATENTS Name Date Lilienfeld Dec. 15, 1925 Osborne Dec. 24, 1935 Edwards May 26, 1942 Freeman Oct. 13, 1942 Fries Dec. 15, 1942 Freeman June 13, 1944 FOREIGN PATENTS Country Date Great Britain Nov. 28, 1941 

